Within the context of stringent legal regulations with regard to the pollutant emissions generated by motor vehicles, one important measure is to keep the pollutant emissions generated during the combustion of the air/fuel mixture in the respective cylinder of the internal combustion engine low. A further measure is to also use, in the case of internal combustion engines, exhaust-gas aftertreatment systems which convert the pollutant emissions generated during the combustion process of the air/fuel mixture in the respective cylinder into non-harmful substances. For this purpose, use is made of exhaust-gas catalytic converters which convert carbon monoxide, hydrocarbons and nitrogen oxides into non-harmful substances.
Both the targeted influencing of the generation of pollutant emissions during the combustion and also the conversion of the pollutant components with a high level of efficiency by means of the exhaust-gas catalytic converter necessitate a very precisely set air/fuel ratio in the respective cylinder.
In particular in the context of an increasingly very close-coupled arrangement of the exhaust-gas catalytic converters and also with regard to correspondingly specific legal regulations in individual countries, cylinder-specific precise setting of the air/fuel ratio is increasingly important because the individual exhaust-gas batches undergo only relatively poor mixing owing to the short mixing path.
Increasingly stringent legal regulations with regard to the emission of limited pollutants make it necessary to allow a small tolerance in the air/fuel ratio between the individual cylinders. A large uneven distribution and an absence of compensation leads to a considerable impairment of emissions, or even to noticeable drivability problems.
Furthermore, there are legal regulations for detecting the cylinder-selective uneven distribution in the air/fuel ratio, which leads to the exceedance of predefined emissions limit values, in a progressively increasing proportion of vehicles in relation to the vehicle fleets of the respective manufacturers.
For the purpose of cylinder-specific precise setting of the respective air/fuel ratio in the respective combustion chambers of the respective cylinders, it is known from DE 10 2005 009 101 B3 for a measurement signal of an exhaust-gas probe to be detected, and assigned to the respective cylinder, at a predefined sensing crankshaft angle in relation to a reference position of the piston of the respective cylinder. By means of in each case one controller, a controller value for influencing the air/fuel ratio in the respective cylinder is determined as a function of the measurement signal detected for the respective cylinder. When predefined first conditions are met, which include a first temperature range of a temperature which is representative of a temperature of the respective injection valve, and which include the presence of a virtually steady operating state, a first adaptation value is determined as a function of the controller value.
When predefined second conditions are met, which include a predefined second temperature range of the temperature which is representative of the temperature of the respective injection valve, and which include the presence of a virtually steady operating state, a second adaptation value is determined as a function of the controller value.
A corrective value for influencing the air/fuel ratio in the respective cylinder is determined as a function of the first and/or second adaptation value as a function of the temperature which is representative of the temperature of the respective injection valve.
From DE 10 2004 004 291 B3, it is known to use cylinder-specific lambda control, the intention of which is to minimize the individual deviations of the respective cylinder-specific air/fuel ratios with respect to a mean air/fuel ratio. A measurement signal of an exhaust-gas probe arranged in an exhaust tract, said measurement signal being characteristic of the air/fuel ratio in the respective cylinder, is detected at a predefined crankshaft angle with respect to a reference position of the piston of the respective cylinder and is assigned to the respective cylinder. By means of the cylinder-specific lambda control, an actuation variable for influencing the air/fuel ratio in the respective cylinder is generated as a function of the measurement signal generated for the respective cylinder. The predefined crankshaft angle is adapted as a function of an instability criterion of the controller.
DE 10 2006 026 390 A1 discloses an electronic control device for the control of the internal combustion engine in a motor vehicle, having a running irregularity determination unit and having an injection quantity correction unit, wherein a defined group of cylinders is assigned one lambda probe. The injection quantity correction unit is configured such that the injection quantity of one cylinder, which is to be tested, of the defined group can be adjusted in the lean direction by a difference adjustment value assigned to a running irregularity difference value, and the injection quantity of at least one of the other cylinders assigned to the same lambda probe can be correspondingly adjusted in the rich direction, such that overall, a predefined lambda value of said group, preferably a lambda value of at least approximately 1, is attained. The injection quantity correction unit is also configured such that, in this way, a cylinder-specific difference adjustment value can be set for each cylinder of the defined group, and that cylinder-specific correction values can be determined by virtue of the cylinder-specific difference adjustment values being set in a ratio with respect one another.